This invention relates to spark timing controls for spark ignited internal combustion engines and particularly to such a control which substantially eliminates the phenomenon of tip-in knock. Tip-in knock is that knock or ping which occurs almost immediately upon the sudden opening of the vehicle throttle valve with the resulting sudden increase in pressure within the engine intake manifold. It is a momentary phenomenon and is thus not subject to control by closed loop knock sensing systems, since the knock occurs and often ends before the system can properly react. The result of the application of a closed loop knock control system to tip-in knock mmay thus be that the knock is not eliminated but the spark timing is uselessly and detrimentally retarded after the knock occurs.
The prior art shows awareness of the problem of tip-in knock and is in substantial agreement about a general approach to its elimination. Since it occurs so quickly, it must be anticipated by the sensing of a tip-in event: that is, a sudden increase in throttle opening or pressure within the intake manifold. There are many prior art patent references which show systems effective to sense an engine tip-in event and retard engine spark timing as quickly as possible given the physical limitations of the apparatus disclosed in order to prevent engine knock. Unfortunately, the spark retard has an undesirable effect as well in that it reduces engine power just at the time when that power is most desired: during a vehicle acceleration or sudden increase in engine load. It is, therefore, very noticeable and irritating to the vehicle operator. The problem of obtaining the beneficial tip-in knock eliminating effect of immediate spark retard upon sensing of a tip-in event without the undesirable power loss resulting from that spark retard appears to be unsolved by the prior art.